Aluminum chelates supported by β-quinolyl enolate ligands: synthesis and ROP of ε-CL

Treatment of tautomers of beta-quinolyl ketone-enaminones 1a-6a with AlMe3 afforded beta-quinolyl enolato dialkylaluminium complexes LAlMe2 1b-6b (L = [(2-C9H6N)-CHvC(R)-O-], R = CH3 (1b), Bu-t (2b), Ph (3b), o-tolyl (4b), p-tolyl (5b), p-OMePh (6b)), respectively. 2b reacted with benzyl alcohol to generate the corresponding LAl(OBn)(2) complex 2c. Complexes 1b-6b and 2c were characterized by H-1 and C-13 NMR spectroscopy, elemental analyses and single crystal X-ray diffraction analyses. All complexes were tested as catalyst precursors for ring-opening polymerization of e-caprolactone (epsilon-CL). The results indicated that LAlMe2 (1b-6b) exhibited good activity towards the ROP of epsilon-CL in the presence of benzyl alcohol at 80 degrees C, and LAl(OBn)(2) 2c exhibited higher catalytic activity in the absence of alcohol than 1b-6b for the ROP of epsilon-CL. However, both polymerizations were less controlled. Kinetic studies showed that the polymerization reaction catalyzed by 1b-6b and 2c proceeded with first-order dependence on the monomer and took place through coordination-insertion.